1. Field of the Invention
The present invention concerns the field of mobile telephony and more particularly the field of so-called machine-to-machine communication modules. However, it can apply to any wireless telephone communication device.
2. Description of Related Art
Originally, in cellular mobile telephony networks, wireless telephone communication devices consisted of simple handsets for transmitting voice by means of a cellular radio network, the voice being transmitted by a circuit switching surface. Very quickly, the simple transportation of the voice proved insufficient, and the terminals were provided with means for communicating data according to packet switching protocols such as the IP protocol (Internet Protocol defined by RFC 791). These developments gave rise to various generations of communication standards such as GPRS (General Packet Radio Service), EDGE (Enhanced Data Rates for GPRS Evolution), UMTS (Universal Mobile Telecommunications System), and HSUPA (High Speed Uplink Packet Access).
The packet switching service is implemented by the GPRS subsystem, GPRS designating, according to the context, packet mode, or forms of encoding and then modulation (CS1.4, GMSK) of the symbols on the radio channel. EDGE is a form of packet mode that is distinguished from GPRS only through different encodings and modulation (MCS1.9, 8-PSK) of the data on the radio channel; the entire protocol stack on top of the radio channel is identical. Thus, unless indicated to the contrary, GPRS will designate the packet switching service independently of the radio access technology on the basis of GSM.
Whereas GSM networks basically provide the circuit switching service, the packet switching service is for its part dynamic. The network operator can activate it in some cells only, or deactivate it at certain times of the day in order to release resources, in particular radio resources, for the circuit switching service. This functioning is well suited to conventional mobile telephony usage by a human being.
In this context, the GSM standards provide for a selection of the base station to which the mobile connects on the basis of the quality of the circuit switching service. These mechanisms do not take into account availability or the characteristics specific to the packet switching service.
Use is also being made more and more of GSM networks in a so-called machine-to-machine context. In this context, equipment is provided with a GSM communication module that it uses for communicating with other equipment or essential services. The GSM communication module is then managed and controlled by an application rather than by a human user. These applications have given communication requirements that must absolutely be satisfied for correct functioning of the application. Even if some of these applications may use the circuit switching service, it is generally essential for the packet switching service to be operational. In addition, some characteristics of this packet switching service may be necessary for the correction functioning of the application.
In this context, it is detrimental for the mobile communication module of a system to connect to a cell not having available a packet switching service possessing all the characteristics necessary to the application. And this is all the more true if such a cell is available in the environment of the communication module.